It is an accepted axiom, today, that land is becoming scarce. As the population increases more and more land is being used for habitable structures. The situation has become quite real and critical particularly in coastal areas or low lying areas adjacent rivers and lakes where the characteristics of the soil are such that it is not capable of supporting substantial structural loads such as are imposed by high rise office buildings, apartments, theaters, auditoriums and the like. Typical examples of areas where the noted soil condition exists would be the areas of New Orleans, Louisiana, Washington, D.C. and parts of the New Jersey coast where much of the land area is low lying swamp totally incapable of supporting structural loads and where even artificial fill does not materially improve the situation since the size and weight of structures built on so-called "fill land" are inherently limited by the nature of the area when filled.
Recently, too, a number of projects have been proposed wherein sizeable structures will be built in coastal waters adjacent land areas. One such proposal involves construction of a nuclear power plant off the New Jersey coast. Other proposals involve so-called "offshore" drilling for oil and the even more recently innovated unloading docks for recently developed "super tankers" which are so huge as not to be able to enter coastal parts and therefore must be unloaded "at sea" at offshore docking and pumping stations.
In effecting construction of structures on non-land or in areas of unstable land, the construction industry has resorted to the practice of placing such structures on a multiplicity of supports known as piles. These piles are driven into the ground by the use of mechanical means such as pile drivers, jet pumps, etc., to a sufficient depth that the lower end portion of the pile is embedded in substrata capable of supporting load both compressive and lateral bending loads transferred through the pile from the supported structure. One method of determining the capability of a pile to support loads is to measure the amount of penetrating movement axially of the pile each time the pile is struck at its top end by some type of impact device of known characteristics. When the rate of axial movement decreases to zero or to a predetermined rate per impact, its load carrying capacity can be determined by known engineering calculations. Obviously, it can readily be deduced that the number of piles to be driven to support a given structure becomes the sum total of the structural load as related to the ability of individual piles to carry load times the number of piles driven.
The pile support system is readily adaptable to support many and varied types of structures from apartments and office buildings to offshore drilling rigs and docking facilities and is widely used both here and abroad. However, as might be expected, there are problems connected with the techniques, one of the most pressing ones being the matter of pile length, as it is necessary to go further and further down into appropriate load supporting substrata. The answer to this would appear to be relatively simple-- use longer piles. Unfortunately, however, there are practical limitations on pile length imposed by transport problems, limitations on driving equipment, handling equipment, etc., all of which more or less fix the maximum length of any given pile.
The alternative route to increasing pile length to unmanageable proportions, is to adapt a range of pile lengths which can be readily handled and to subsequently join the individual lengths by some type of on-the-site effected connection means. This alternative has been explored in a number of ways.